1. Field of the Invention
The present invention relates to an electric braking device in which a brake force is generated when a brake element is pushed to a rotating member by operating an electric motor according to an electric signal, and in which the response property is excellent at the beginning of braking operation and the force transmitting efficiency is high after a brake pad and the rotating member are frictionally engaged with each other.
2. Description of the Related Art
An electric braking device is well known in which an electric motor is operated according to an electric signal so that a brake element (brake pad) is pushed to a rotating member (brake rotor) so that a brake force is generated. An example of the electric braking device is disclosed in JP-W-10-504876.
This electric braking device is composed as follows. Rotation of the electric motor is reduced by the reduction device and converted into a liner motion, so that the brake pad opposed to the brake rotor is moved to the brake rotor so as to conduct braking operation.
In the electric braking device described in the above patent publication, the force transmitting and converting mechanism for converting the torque of the electric motor into a pushing force for pushing the brake pad is composed of a roller screw, the force transmitting efficiency of which is high, which is used instead of a force transmitting and converting mechanism composed of a simple screw and nut. However, compared with the simple screw and nut mechanism, the roller screw mechanism is disadvantageous in that a large space is required for housing the electric motor and speed reduction mechanism, so that it becomes difficult to miniaturize the electric braking device. Further, the roller screw is relatively expensive. Therefore, it is difficult to decrease the cost of the electric braking device.
Another electric braking device is described in JP-W-8-510316.
The electric braking device described in the above patent publication includes a gear transmitting device, which is arranged between the electric motor and the brake pad, for pushing the brake pad to the rotating member (brake rotor). There are provided two clutch mechanisms in this gear transmitting device. When the first clutch mechanism is connected and the second clutch mechanism is disconnected, it is possible to obtain various approach speeds and fastening forces. After that, when the first clutch mechanism is disconnected and the second clutch mechanism is connected, it is possible to obtain a higher fastening force, that is, it is possible to obtain a higher brake force. This braking device is advantageous in that the brake pad can be quickly moved at the beginning of braking operation and further when the clutch is changed over after the braking operation, it is possible to obtain a higher fastening force. However, the above braking device is disadvantageous in that the structure becomes complicated and it is difficult to miniaturize the braking device because the force transmitting and converting mechanism is composed of the gear mechanism and two clutches.